Thermoplastic birefringent multilayer optical films are generally formed by layering extruded polymers in feedblocks. In some manufacturing processes, depending on the size of the feedblock, processing conditions, and thickness of the extrudate, shear forces on the outer layers passing through the feedblock may be significant. This can cause layer breakup in the outer layers, often making the ultimate films unusable for their desired purpose. To protect the film throughout manufacturing, thick protective boundary layers or thick skin layers are provided.